This invention relates generally to apparatus and methods for use in the retreading or recapping of tires, and more specifically relates to apparatus and methods for effecting a high quality uniform seal between the tire casing and a curing envelope which covers the tire and retread strip to exclude undesired gases and steam during the heat and pressure cure stage of the recapping process.
In recent years, a method of retreading tires, sometimes referred to as moldless retreading, has gained increasing acceptance in the recapping industry. According to this method, a strip of pre-cured and pre-molded or an uncured tread is applied to a worn tire casing or carcass which has been previously prepared, as by buffing. A layer of suitable binding material is provided between the tread strip and the surface of the tire, commonly an uncured cushion gum. A thin layer or layers of cement may be used to help secure the tire casing, cushion gum and tread strip to one another to provide a temporary assembly for subsequent heat curing.
The aforementioned assembly of casing, tire tread and rubber or rubber-like cushion gum, prior to curing, is enclosed at least partially in a so-called curing envelope, which comprises a relatively strong flexible and resilient material such as a rubber, or plastic. The assembly is then placed in a heating oven or autoclave, and subjected to suitable temperatures and pressures for a period adequate to effect a full cure at the cushion gum bonding zone, i.e. a cure between the tread and the tire casing as will assure a fully satisfactory bond. During the heat cure step the protective envelope, the space within which is connected to a pressure source lower than that in the oven (which can be a vent to atmosphere), serves to keep gases and steam away from the materials being cured, as such gases or steam can interfere with formation of a fully cured and effective bond.
In certain portions of the prior art, including in Carver, U.S. Pat. No. 3,236,709, an operation of the aforementioned nature is carried out with the tire casing mounted on a suitable rim with or without removable flanges, and with an internal air tube or other arrangement enabling pressurization of the interior of the tire carcass--this in order to maintain a firm contact between the curing envelope and the external wall of the tire casing and the rim flanges or other flanges. This has as its objective to assure a relatively good seal between the curing envelope and the casing, since in the absence of such seal, leakage of hot gases, including steam, into the curing space can markedly affect the quality of the bond between the tread and the tire carcass. Such an arrangement, however, has the detrimental effect of preventing or at least limiting heat from reaching the interior space of the tire carcass, which slows the cure rate and can also retard uniformity in heating at the cure zone.
In U.S. Pat. No. 4,274,897 to Barefoot, these shortcomings are recognized, and a construction is set forth which in certain embodiments of the invention endeavors to provide an external curing envelope about the outer surfaces of the tire carcass, which envelope is sealed to the tire by means cooperating with the outer tire side wall, so that it is not necessary to use an inner inflatable tube or rim, thereby permitting heat to reach the interior portion of the tire casing. In most of the embodiments of Barefoot, however, the seal between envelope and tire carcass is effected at the side wall portion of same, where experience has shown that a seal can only be maintained with great difficulty--in view of the irregularities of the said wall, resulting from not only wear, but from the embossments which usually appear on same. While in FIGS. 8 and 9 of Barefoot, a rim engages with a portion of the tire bead (which is superior to engagement at the side wall), the two sealing rims are biased by a plurality of springs drawing same toward each other, and in some instances against intermittent spacers. This tends to produce a distortion of the tire body; it cannot provide a positive controllable pressure at the sealing zone; and therefore can result in inferior sealing.
A somewhat similar arrangement is taught in Barefoot, U.S. Pat. No. 3,752,726.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide apparatus and method for use in sealing cure envelopes to tire casings undergoing retreading, which enable an exceedlingly effective seal between the sealing envelope and the tire carcass, thereby assuring that a quality retread results during the subsequent heat cure of the assembly.
It is a further object of the present invention, to provide apparatus of the foregoing character, which may be simply and effectively employed by relatively unskilled personnel, and yet provide the fully effective seal aforementioned.
It is a still further object of the invention, to provide apparatus and method as aforementioned, which can be used to seal a pair of sealing envelopes to the tire casing, respectively to enable sealing covers for both the outer and inner surfaces of the tire casing.
It is a yet further object of the present invention, to provide apparatus and methodology as aforementioned, which, while providing a fully effective seal for the exterior facing portions of a tire carcass, and as optionally desired for the internally facing portions of the carcass, yet enable full access of heat to the interior annular reaches of the casing during the heat curing process.